Subarachnoid bolts for measuring or monitoring intracranial pressure have been known for some time. One of the more widely utilized bolts, commonly referred to as a "Philly" bolt, is comprised essentially of stainless steel or similar material and includes an external screw thread at its lower end which is intended to be screwed into a twist drill hole formed in a patient's skull. The extreme end of the bolt enters the subarachnoid space over the cerebral hemisphere.
While known subarachnoid bolts have met with some success, they have also suffered from many problems particularly with patients with very thin skulls such as neonatal patients. With such patients and in many other cases, it is extremely difficult and sometimes impossible to secure the bolt to the skull by screwing the same thereto.